Sleep Cycle Calculator
Suggested bedtimes from a wake time, or suggested wake times from a bedtime — both built on 90-minute sleep cycles + a fall-asleep buffer.
Result
General calculation reads
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How to use this calculator
- Enter target wake time.
- Adjust fall-asleep time if you tend to lie awake longer.
- Pick the bedtime closest to your usual schedule.
About this calculator
Sleep happens in ~90-minute cycles (Carskadon & Dement, NREM/REM staging). Waking at the end of a cycle (after 4.5, 6, 7.5, or 9 hours of sleep) feels less groggy than waking mid-cycle. Mode 1 subtracts cycles back from your target wake time; mode 2 adds cycles forward from your bedtime. Both account for the time it takes to fall asleep (sleep latency, typically 10-20 minutes per the American Academy of Sleep Medicine).
Frequently asked
Is the 90-minute cycle exact?+
How many cycles do I need?+
Why does waking mid-cycle feel bad?+
Doesn't this change with age?+
Should I stick to the exact bedtime?+
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